Physical and chemical stability is a major concern in the application of heterogeneous catalysts in aqueous phase reactions. Traditional SiO2 or Al2O3 based catalyst supports are prone to prone to disintegration or attack when used in an aqueous solution, which usually results in loss of mechanical strength of the catalyst body that is targeted for a long-term industrial application. In laboratory and industrial applications, the mechanical strength of heterogeneous catalysts is generally evaluated by crush strength, wherein increasing crush strength values are generally indicative of improved mechanical strength of the support or carrier.
Catalytic supports or carriers may comprise a variety of materials, such as zirconium oxide, also referred to as zirconia, which is a known high temperature refractory material with extensive industrial applications. It is also a known catalyst support material because of its high physical and chemical stability and moderate acidic surface properties. Nonetheless, the use of zirconia as a supporting material for heterogenous catalysts has limited application due to its relatively high cost and difficulties in forming certain shapes from this material. Furthermore, the zirconia often undergoes a phase transformation that results in a substantial change in structure, and loss of surface area and pore volume. This reduces the strength and durability of the zirconia. To inhibit phase transformation effects, stabilizing agents are used to maintain preferable phases.
One non-exhaustive example of technology directed to making zirconia catalyst supports is described in WO 2007/092367 (filed by Saint-Gobain), which describes a formed ceramic body comprising tetragonal zirconia as the primary phase with a surface area greater than 75 m2/g and a pore volume of over 0.30 mL/g. In one aspect of the invention, a process for making a zirconia carrier is described and is further defined by the use of inorganic or organic binder(s) and/or stabilizing agents. The stabilizing agents may be selected from among silicon oxide, yttrium oxide, lanthanum oxide, tungsten oxide, magnesium oxide, calcium oxide and cerium oxide.
A recent trend is to use plant or animal-derived compounds (e.g. biomass) as the feedstock to make valuable chemicals that are typically derived from petroleum. One example is the use of glycerin (glycerol) to make propylene glycol (PG), which is extensively used in many applications such as the production of polyester, polyurethane polymers and as anti-freeze and de-icing compounds, and therefore remains a useful chemical. Other examples of commercially important intermediate chemicals that can be derived from biomass and subsequently converted to high value chemicals include use of sugars or sugar alcohols (e.g. glucose or sorbitol) to make shorter-carbon chain sugar alcohols through hydrogenation and hydrogenolysis. In both processes, hydrogen is added to the target compound in the presence of a catalyst and under aqueous conditions. Hydrogenolysis is a process that involves the breakage of chemical bonds, such as a carbon-carbon or carbon-oxygen bonds, through addition of hydrogen.
One non-exhaustive example of a catalytic hydrogenation process is described in U.S. Pat. No. 6,982,328 (Werpy et al.). Werpy et al. discloses an invention that includes a process of forming glycerol, ethylene glycol, lactic acid and propylene glycol from plant matter by adding water, heating and filtering the plant matter. In one aspect of the invention, a reduction step (400) can comprise catalytic hydrogenation, exposing saccharides to a catalyst comprising a support and one or more members of the groups consisting of Ru (ruthenium), Ni (nickel), Pt (platinum) and Pd (palladium). The catalyst support can comprise carbon and/or other insoluble support material, such as titania and zirconia.
An additional non-exhaustive example of related technology is described in U.S. Pat. No. 6,900,361 (Elliott et al.). Elliott et al. discloses an invention that includes a process for converting lactose into polyols that includes a hydrogenation step that involves heating the hydrolyzate in the presence of hydrogen and a catalyst. The hydrogenation catalyst may be any type of catalyst capable of initiating and sustaining hydrogenation of a monosaccharide. Such catalysts are well known and typically are metal catalysts such as Ru (ruthenium), Ni (nickel), Co (cobalt), Cu (copper) and alloys thereof. The metal catalysts may be provided on various support substrates such as titania, zirconia, alumnia, silica, alumina/silica and carbon. According to certain embodiments, the catalyst support is especially stable in aqueous medium or phase chemical reaction conditions. According to Elliot et al., exemplary stable supports include titania in the rutile form, zirconia in the monoclinic form, high-surface area granulated carbons, or boehmite.
It has now been found that zirconia promoted with a polyacid or similarly functioning promoter material yields a zirconia-based support or catalyst with improved physical properties for extrusion and/or use as a carrier or support for a catalyst in industrial applications performed in an aqueous environment, including the conversion of sugars, sugar alcohols or glycerol into polyols and/or shorter-carbon chain chemicals and materials for use in other applications. The improvement to mechanical strength of the catalyst support or carrier inhibits metal leaching into an aqueous solution, improving the mechanical strength and stability of the support or carrier in such conversion reaction processes.
Certain embodiments of the invention represent improvements in supports or carriers utilized in catalysts and as employed in conversion reactions in which a catalyst is deployed.